I. Field of the Invention
This invention relates to promoters used for expressing foreign genes introduced by genetic engineering techniques into cells of monocotyledonous (monocot) plants, especially cereals such as wheat, barley, maize, oat and rice.
II. Description of the Prior Art
Genetic engineering is a procedure in which desired genes are inserted and stably integrated into the host genome followed by regeneration and selection for transformed plants using tissue culture methods. The development of plant transformation techniques has opened up the possibility to introduce and express genes of diverse origins in plants and thereby created a powerful tool to supplement and complement traditional plant breeding.
Significant progress has recently been made in the genetic transformation of cereals, such as wheat (see, for example, Nehra, N. S., et al., "Wheat Transformation: Methods and Prospects," Plant Breeding Abstracts, 65(6):803-808, 1995, the disclosure of which is incorporated herein by reference). In particular, the inventors of the present invention have achieved the genetic transformation of wheat by biolistically delivering genes into isolated scutella, the starting explant for an enhanced regeneration system (Nehra, N. S., et al., "Self-fertile Transgenic Wheat Plants Regenerated From Isolated Scutellar Tissues Following Microprojectile Bombardment With Two Distinct Gene Constructs", The Plant J., 5(2):285-297, 1994, the disclosure of which is also incorporated herein by reference).
With the development of gene transfer techniques, the remaining limitation for commercial exploitation of genetic transformation technology in wheat and other monocot plants is the lack of efficient promoters that will direct foreign gene expression in transgenic wheat plants. Many of the most commonly used promoters employed to transform dicot plants show low activity in cereal cells. A rice actin promoter, which transiently expresses high activity of marker genes in cultured barley cells (Chibbar, R. N., et al., "The effect of Different Promoter-Sequences on Transient Expression of GUS Reporter Gene in Cultured Barley Hordeum vulgare L. cells", Plant Cell Reports, 12:506-509, 1993), has been successfully used in the production of transgenic wheat. Moreover, a promoter comprising the 5'-region of a rice RAc1 gene for use in rice is disclosed in PCT patent publication WO 91/09948 filed in the name of Cornell Research Foundation and published on Jul. 11, 1991; and a nucleic acid promoter fragment comprising the 5' flanking promoter region of the Em structural gene in wheat is disclosed in U.S. Pat. No. 5,139,954 issued on Aug. 18, 1992.
However, there is a need for more effective promoters for use in cereal plants, especially wheat, barley, maize, oat and rice.